From 588ddc7a3400d4462253fbc13a2ccb211aa6a00e Mon Sep 17 00:00:00 2001
From: Brent Yorgey <byorgey@LVN513-12.cis.upenn.edu>
Date: Fri, 15 Apr 2011 15:22:54 -0400
Subject: [PATCH] Update comment on fmapDefault to note that it only works for Traversable
instances with a given definition of traversable, and NOT for instances
with only sequenceA given.
---
Data/Traversable.hs | 5 ++++-
1 files changed, 4 insertions(+), 1 deletions(-)
diff --git a/Data/Traversable.hs b/Data/Traversable.hs
index 2bdc1bc..062d1a0 100644
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b
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| 170 | 170 | mapAccumR :: Traversable t => (a -> b -> (a, c)) -> a -> t b -> (a, t c) |
| 171 | 171 | mapAccumR f s t = runStateR (traverse (StateR . flip f) t) s |
| 172 | 172 | |
| 173 | | -- | This function may be used as a value for `fmap` in a `Functor` instance. |
| | 173 | -- | This function may be used as a value for `fmap` in a `Functor` |
| | 174 | -- instance, provided that 'traverse' is defined. (Using |
| | 175 | -- `fmapDefault` with a `Traversable` instance defined only by |
| | 176 | -- 'sequenceA' will result in infinite recursion.) |
| 174 | 177 | fmapDefault :: Traversable t => (a -> b) -> t a -> t b |
| 175 | 178 | {-# INLINE fmapDefault #-} |
| 176 | 179 | fmapDefault f = getId . traverse (Id . f) |
